1. Field of the Invention
The present invention relates to a quantum dot infrared detection device and a method for fabricating the same, in which a quantum dot is doped or a quantum dot layer itself is formed as an electron moving channel for detecting a weak infrared signal by using the quantum dot channel.
2. Background of the Related Art
Though an infrared ray, with a wavelength ranging from approx. 5xcx9c6 xcexcm to a few tens of xcexcm, may be detected in a variety of methods depending on materials of a device for detecting the infrared ray, the infrared device should be cool down to at least 77K, for operating the infrared device at the room temperature for detecting a good quality signal. However, because the cooled down method is a very complicated and the cooling down device is expensive and bulky, the method in which the device is cooled down could not be spread widely, but used for special applications. Therefore, recently, in order to improve such a disadvantages, there have been many researches for a device for detecting an infrared ray.
The operation principle of the device for detecting an infrared ray will be explained. Upon directing an infrared ray onto a quantum dot, a portion of the infrared ray corresponding to an inter-subband transition energy of the quantum dot is absorbed, and converted into electrons(photo current), to facilitate detection of the infrared ray. A structure in which a quantum dot and a pin diode are bonded as shown in FIG. 1 is well known as a related art quantum dot infrared detection device, and recently, a structure in which a quantum dot and HEMT(High Electron Mobility Transistor) are bonded as shown in FIG. 2 has been developed. In the device as shown in FIG. 1 of a type in which the quantum dot and the pin diode are bonded, the electrons produced by an absorbed infrared ray equal to a sub-band energy difference of the quantum dot generates a photo current by a reverse bias of an existing pin detector. However, the device is known that detection of extremely weak signal is almost impossible at a room temperature because of a leakage current coming from a dislocation of an extremely low density which may occur in formation of a quantum dot, or of a leakage current caused by a recombination-generation current generated by a reverse voltage in the pin diode structure. Thus, application of the device to a system which is operated at a room temperature, such as a general use infrared CCD camera, or to a system using a simple cooling system is almost impossible, because the device should be operated only at a low temperature(below approx. 100K) at which the leakage current is low for obtaining a signal characteristic, In the meantime, a device of a form the quantum dot and the HEMT are bonded shown in FIG. 2 is expected to be operative at a room temperature because an electron density in a quantum dot state is in a form of delta function, and a difference of a ground state and a first excited state is greater than a thermal energy at the room temperature in a case an infrared ray corresponding to a subband energy difference is incident from a front or back of a quantum dot region. Particularly, as shown in FIG. 3, this structure is advantageous in that the infrared ray is absorbed in the quantum dot to cause a inter-subband transition, electrons excited by which are tunneled through an undoped GaAs channel, and captured by a voltage difference between a first terminal and a second terminal, or captured by a voltage difference between terminals in the quantum dot region. That is, by transmitting through a clean channel which can transfer the weak signal detected at the quantum dot without a loss of the electrons, the signal can be separated from an environmental noise or the leakage current. In this instance, overall characteristics of the signal is dependent on a signal of the electrons captured at the undoped GaAs channel. because the undoped GaAs channel region restricted by the doped AlGaAs barrier provide a high mobility for moving the electrons without any loss.
However, the above structure causes a problem in that the electrons captured at the quantum dot by the infrared ray absorption are absorbed by other quantum dots or lost in a course of transfer to the channel region, that drops an overall efficiency. That is, such a loss can drop a performance of the detection device, sharply. Another problem is that an externally doped impurity layer(barrier layer) should be disposed in the vicinity of the quantum dot because a ground state should be filled by supplying electrons thereto. That is, though it is possible theoretically, it is very complicated condition that the impurity layer is precisely controlled for supplying optimal electrons to the quantum dot, and disposing the impurity layer in the vicinity of the quantum dot for obtaining uniform characteristics over a large area. And, though the doped impurity layer(barrier layer) should be etched uniformly for the optimal supply of electrons to the quantum dot, the uniform etching of the impurity layer is not easy.
Accordingly, the present invention is directed to a quantum dot infrared detection device and a method for fabricating the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a quantum dot infrared detection device and a method for fabricating the same, of which structure and fabrication process are simplified for enhancing uniformity.
Another object of the present invention is to provide a quantum dot infrared detection device and a method for fabricating the same, which can provide a two dimensional uniform array device for application to an imager.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the quantum dot infrared detection device includes a buffer layer or an undoped barrier layer on the substrate, a doped quantum dot part on the buffer layer or the undoped barrier layer, an undoped barrier layer on the quantum dot part, and electrodes on regions of the undoped barrier layer.
A doped contact layer is further provided between the undoped barrier layer and the electrodes.
A p type doped layer is formed under the electrode below the p type doped contact layer.
The quantum dot part includes a multilayered structure of alternative stacking of a quantum dot and a separating layer.
In another aspect of the present invention, there is provided a method for fabricating a quantum dot infrared detection device, including the steps of (1) forming a buffer layer or an undoped barrier layer on a substrate, and forming a doped quantum dot part having quantum dots and separating layers stacked alternatively, (2) forming an undoped barrier layer on the quantum dot part, and (3) forming doped contact layers in regions of the undoped barrier layer, and forming electrodes thereon.
The substrate is fonned of one selected from GaAs, InP, Si, Al2O3, and GaN, the undoped barrier layer is formed of one selected from AlyGa1xe2x88x92y As (where, 0xe2x89xa6yxe2x89xa61), AlInP, InP, Si, GaN, and AlGaN, the quantum dot is formed of one selected from InxGa1xe2x88x92xAs (where, 0 less than xxe2x89xa61), SiGe, InnGa1xe2x88x92nN (where, 0 less than nxe2x89xa61), the separating layer is formed of one selected from AlkGa1xe2x88x92kAs (where, 0xe2x89xa6kxe2x89xa61), Si, AlmGa1xe2x88x92mN (where, 0xe2x89xa6mxe2x89xa61), InP, AlInP, and the buffer layer is formed of GaAs, AlGaAs, InP, and GaN.
The quantum dot is of xe2x80x98nxe2x80x99 type, and has an impurity concentration of 1015/cm3 xcx9c1018/cm3.
The aforementioned quantum dot infrared detection device and method for fabricating the same have the following advantages.
By doping the quantum dots in the quantum dot part with impurities, the quantum dot part itself is made to absorb infrared ray and serve as a channel for transferring electrons generated by the infrared ray absorption, for enhancing device performance and a device uniformity, and simplifying a device structure and a device fabrication process.
Therefore, the quantum dot infrared detection device and method for fabricating the same is suitable for application to imagers, such as CCD camera, as it permits to provide two dimensional uniform array device, and can reduce a cost since a process for producing uniform devices can be simplified.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.